Cutting assembly

ABSTRACT

This disclosure relates to a cutting assembly comprising a circular disk cutter (18). A plurality of cutting elements (22) and a corresponding quantity of tool holders (24) are arranged around a circumferential surface of the disk cutter. Each tool holder is at least partially laterally offset with respect to the circular body.

FIELD OF THE INVENTION

The present disclosure relates to mining and excavation machines. Inparticular, it relates to a cutting assembly for a rock excavationmachine.

BACKGROUND

Many types of rock formations are available around the world as largedeposits, commonly known as slabs. Various types of mining equipment aredeployed in above ground quarries in order to extract the slabs from theground. The slabs are retrieved using specialist equipment, typicallydragged from their resting place by large and very powerful vehicles.Rock slabs may weigh up to 40 tons (40,000 kg). Processing, such aspolishing, may take place on site, or alternatively the slabs may betransported off site for cutting into appropriately sized pieces fordomestic and industrial use.

The same equipment used above ground may not always be directly usablewithin the confined space of a subterranean mine.

It is an object of the invention to provide a compact and versatilecutting assembly to facilitate the mining and extraction ofgeometrically or non-geometrically shaped blocks of specific rockformations, and one that may be used above or below ground.

SUMMARY OF THE INVENTION

According to the invention, there is provided a cutting assembly for arock excavation machine comprising: a base unit, one or more moveablesupport arms extending from the base unit, a drive spindle rotatablymounted to the or each moveable support arm, a disk cutter fixed aboutthe drive spindle such that rotation of the drive spindle causes acorresponding rotation of the disk cutter, the disk cutter comprising acutter body, a plurality of cutting elements and a correspondingquantity of tool holders, one for each cutting element, the cuttingelements and tool holders being arranged around a circumferentialsurface of the cutter body, in which each tool holder is at leastpartially laterally offset with respect to the cutter body.

In some embodiments, successive tool holders around the circumferentialsurface are laterally offset in alternating first and second directions.

Optionally, each tool holder comprises a proximal portion and a distalportion meeting at an intersection. Preferably, the distal portion islaterally offset with respect to the proximal portion.

Preferably, each cutting element is mounted in the distal portion of thetool holder.

Optionally, the cutting assembly further comprises hard-facing materialon or near each tool holder.

In an embodiment, the hard-facing material is different to material ofeach cutting element.

The hard-facing material may be located on a leading face of each toolholder. Additionally or alternatively, the hard-facing material may belocated on a trailing face of each tool holder. Additionally oralternatively, the hard-facing material may be located on or in thecircumferential surface of the circular body.

Optionally, at least one cutting element has a strike tip having aconical or pyramidal profile.

Optionally, at least one cutting element has a strike tip having ahemi-spherical profile.

Optionally, at least one cutting element has a strike tip having aballistic profile.

Optionally, at least one cutting element has a truncated strike tip witha planar apex.

Combinations of shaped cutting elements may be used, on a single diskcutter or on one or more of multiple disk cutters if used.

Each cutting element may be a polycrystalline diamond compact (PDC).

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be more particularly described, by way of exampleonly, with reference to the accompanying drawings, in which

FIG. 1 is a schematic plan view of an underground mine incorporating afirst embodiment of a cutting assembly as part of a long wall miningsystem, and in particular shows the cutting assembly in a horizontalorientation;

FIG. 2 is a schematic end view of the long wall mining system of FIG. 1;

FIG. 3 is a schematic plan view of an underground mine incorporating asecond embodiment of a cutting assembly as part of a long wall miningsystem, and in particular shows the cutting assembly in a verticalorientation;

FIG. 4 is schematic end view of the long wall mining system of FIG. 3;

FIG. 5 shows a front elevation view of a first embodiment of a diskcutter;

FIG. 6 shows a front elevation view of a cutting element for use withthe disk cutter of FIG. 5;

FIG. 7 shows a side elevation view of the cutting element of FIG. 6;

FIG. 8 shows a front perspective view of a second embodiment of the diskcutter;

FIG. 9 shows a side elevation view of a plurality of cutting elementsfor use with the disk cutter of FIG. 8;

FIG. 10a is a side elevation view of a first individual cutting elementfrom FIG. 9;

FIG. 10b is a side elevation view of a second individual cutting elementfrom FIG. 9; In the drawings, similar parts have been assigned similarreference numerals.

DETAILED DESCRIPTION

Referring initially to FIGS. 1 to 2, a cutting assembly for slicing intonatural formations 2 underground is indicated generally at 10.

The cutting assembly forms part of a long wall mining system 1, commonlyfound in underground mines. The cutting assembly is a substitute forknown shearer technology, which operates on a mine floor 4, amidst aseries of adjustable roof supports 6. As the shearer advances in thedirection of mining, the roof supports 6 are positioned to uphold themine roof 8 directly behind the shearer. Behind the roof supports 6, themine roof 6 collapses in a relatively controlled manner. Typically, agathering arm collects mined rock at the cutting face and transfers itonto a conveying system for subsequent removal from the mine.

In a first embodiment, indicated in FIGS. 1 and 2, the cutting assembly10 comprises a base unit 12, a pair of spaced apart support arms 14extending from the base unit 12, a drive spindle 16 extending betweenand rotatably mounted to the pair of moveable support arms 14, and aplurality of disk cutters 18 fixed about the drive spindle 16.

In a second embodiment, indicated in FIGS. 3 and 4, a single support arm14 extends from the base unit 12. The drive spindle 16 is supportedcentrally by the single support arm 14, and the plurality of diskcutters 18 is mounted to the drive spindle 16, distributed either sideof the single support arm 14.

In an alternative embodiment, not shown, only a single disk cutter 18 isused.

Preferably, the or each disk cutter 18 is mounted at is centre (i.e.centrally) about the drive spindle 16. However, this is not essential,and the or each disk cutter 18 may alternatively be mounted off-set fromits centre about the drive spindle 16. Optionally, a combination of thetwo arrangements could be used instead. For example, when multiple diskcutters 18 are used in a series, i.e. in parallel next to each otheralong a drive spindle 16, alternating disk cutters 18 may be mountedcentrally about the drive spindle 16. Each centre of the remaining diskcutters 18 may be radially off-set from the point at which the diskcutter 18 is mounted about the drive spindle 16. Other combinations areenvisaged.

The base unit 12 functions as a transport system for the disk cutter 18.The base unit 12 is moveable to advance and retract the disk cutter 18into and out of an operational position, in close proximity to the rockformation 2 to be cut. The speed at which the base unit 12 moves closerto the rock formation 2 is one of several variables determining the feedrate of the cutting assembly 10 into the rock formation 2. The base unit12 (in concert with the roof supports 6) is also moveable sideways, fromleft to right and vice versa, along the long wall of the rock formation2 to be mined.

Each support arm 14 is configured to be moveable into a first and asecond cutting orientation. In the first cutting orientation, best seenin FIGS. 1 and 2, the drive spindle 16 is horizontal. As a result, cutsin the rock formation 2 made by the disk cutter 18 are correspondinglyvertical. In the second cutting orientation, best seen in FIGS. 3 and 4,the drive spindle 16 is vertical. Consequently, cuts in the rockformation 2 made by the disk cutter 18 are correspondingly horizontal.First and second cutting orientations are possible with either first orsecond embodiments mentioned above.

Optionally, the support arm(s) 14 may also be moveable such that thedrive spindle 16 is operable in any cutting orientation between theaforementioned vertical and horizontal, though this is not essential.The support arm(s) 14 may alternatively be configured such that they aremoveable between the first and second cutting orientations but onlyfully operational (i.e. the disk cutter(s) to rotate in order tofacilitate cutting or pulverising of the rock) in the first and secondcutting orientations.

Each support arm 14 is moveable between a first operative position and asecond operative position, in optionally each of the first and secondcutting orientations, according to the depth of cut required. This isindicated by double end arrow A in FIG. 2. For example, in the firstoperative position, the drive spindle 16 is lowered so as to be in closeproximity to the mine floor 4 and in the second operative position, thedrive spindle 16 is raised so as to be in close proximity to the mineroof 8.

Optionally, each support arm 14 may have a first arm portion connectedto a second arm portion by a pivot joint (or alternatively, a universaljoint), each first and second arm portion being independently moveablerelative to each other. This arrangement augments the degrees of freedomwith which the cutting assembly 10 may operate and advantageouslyimproves its maneuverability.

The drive spindle 16 is driven by a motor to rotate at a particularspeed. The power of the motor is typically between 20 and 50 kW per diskcutter 18, depending on the type of disk cutter 18 selected and thecutting force required.

As best seen in FIG. 5, in one embodiment, the disk cutter 18 comprisesa circular body 20 and a plurality of cutting elements 22 arrangedperipherally around the circular body 20. Rotation of the drive spindle16 causes a corresponding rotation of the disk cutter 18. However, thedisk cutter 18 need not be circular and may just be generally circular,for example, depending on its size, an octagonal shaped cutter couldapproximate a generally circular disk cutter. Accordingly, the diskcutter 18 may be hexagonal, octagonal, decagonal etc, or indeed have anynumber of circumferentially extending sides.

The or each disk cutter 18 may further comprise one or more sensors.These sensors may be embedded or integrated into the cutter body 20. Thesensor may be any one of the following: a temperature sensor, a pressuresensor, an X-ray sensor, a gamma ray sensor, an accelerometer, a sensorconfigured to monitor the chemistry of the cutting conditions, or asensor to identify the rock formation or materials for extraction. Insuch an embodiment, the sensors may be coupled to a data harvestingsystem, and potentially also coupled with a data analysis packageon-line or remote from the mining/extraction operation.

In a preferred embodiment, a plurality of disk cutters 18 is arranged onthe drive spindle 16. Typically, six or more disk cutters 18 may beprovided. The disk cutters 18 are preferably regularly spaced apartalong the length of the drive spindle 16, between the pair of spacedapart support arms 14 a, 14 b, or either side of the support arm 14,depending on the embodiment.

The spacing of the disk cutters 18 is selected according to the depth ofcut required and the mechanical properties, e.g. Ultimate TensileStrength (UTS), of the rock formation 2 being cut in order to optimisethe specific cutting energy, which will dictate the required powerconsumption. The aim is to achieve conditions under which the cutmaterial will breakout under its own weight. For example, for a 0.4 mdepth of cut in Kimberlite, the ideal spacing between adjacent diskcutters is around 0.3 m. However, this can be increased or decreaseddepending on the force required for breakout. Preferably, the spacing isadjustable in-situ and may be an automated process or a manual process.The spacing may be remotely adjustable, for example from an operationsoffice above ground. A wedge shaped tool may be used to apply such abreakout force, to assist in rock breakout.

The disk cutters 18 are spaced apart by a gap measuring betweenpreferably 0.01 m and 2 m, more preferably between 0.01 m and 0.5 m. Yetmore preferably, the disk cutters are 18 spaced apart by a gap measuringbetween 10 cm and 40 cm.

The circular body 20 of the disk cutter 18 is typically made from steeland has a diameter of approximately 1000 mm and a thickness (measuredaxially, also considered to be a lateral extent for subsequentdescriptions) of approximately 11 mm. Realistically, such a diameterenables a depth of cut of up to 400 mm. The circular body 20 has a shaftdiameter 23 of between 60 mm and 100 mm, and is sized and shaped toreceive the drive spindle 16.

The diameter (or effective diameter in the case of non-circular diskcutters) and thickness of the disk cutter 18 are selected appropriatelyaccording to the intended application of the cutting assembly. Forexample, cable laying applications would require a disk cutter 18 with asmaller diameter. Robotic arm angle grinders would require a yet smallerdiameter. Tunneling applications though would require a disk cutter 18with a significantly greater diameter and would be adapted accordingly.

In this embodiment, the disk cutter 18 also comprises a plurality oftool holders 24 for receiving a corresponding quantity of cuttingelements 22. In an alternative embodiment, the disk cutter comprises oneor more tool holders.

Preferably though not essentially, each tool holder 24 provides a seatfor one cutting element 22. Preferably, each tool holder 24 is made fromsteel but may alternatively comprise any metal(s) or carbides or ceramicbased materials with a hardness above 70 HV (Vickers Hardness). Eachtool holder 24 may be either permanently connected to the cutter body 20(e.g. using brazing or welding), as in the embodiment shown in FIGS. 5,6 and 7, or it is detachably mounted to the cutter body 20 using aretention mechanism, as in the embodiment shown in FIGS. 8, 9 and 10 aand 10 b. A mixture of brazing, welding and/or mechanical connectionscould be used. Alternatively, the tool holder(s) 24 may be formedintegrally with the body 20 of the disk cutter 18, for example, byforging, powder metallurgy etc.

The retention mechanism may comprise a locking pin arrangement 25 whichis used to secure the tool holder 24 to the cutter body 20. Clamping,shrink fitting etc may alternatively be used. In one embodiment, eachcutting element 22 is rigidly or fixedly supported by one of the toolholders 24. Each tool holder 24 is preferably equi-angularly spacedaround a circumferential surface of the cutter body 20. Each cuttingelement 22 may be secured in place in or on the tool holder 24 usingbrazing. Alternatively, the or each tool holder 24 may be configured torotatably receive a cutting element 22. In such an embodiment, thecutting element 22 and tool holder 24 may be configured such that thecutting element 22 may freely rotate within the tool holder 24, e.g.with a clearance fit, or alternatively be able to rotate within the toolholder 24 only when the cutting element 22 comes into contact with therock formation being mined/excavated, e.g. with a transition fit.

Each of the cutting elements 22 comprise a hard, wear resistant materialwith a hardness value of 130 HV and above. The cutting element 22preferably comprises a superhard material selected from the groupconsisting of cubic boron nitride, diamond, diamond like material, orcombinations thereof, but may be a hard material such as tungstencarbide instead. The cutting element 22 may comprise a cemented carbidesubstrate to which the superhard material is joined.

In one embodiment, the cutting elements 22 are polycrystalline diamondcompacts (PCDs), more commonly found in the field of Oil and Gasdrilling. Such PCDs are often cylindrical and usually comprise a diamondlayer sinter joined to a steel or carbide substrate.

The PCD has a diameter of between 6 mm and 30 mm, preferably between 8mm and 25 mm. For example, the PCD may have a diameter of 13 mm, or 16mm or 19 mm. Preferably, the PCD has a diameter of 16 mm. A combinationof diameters may be used in a disk cutter.

Each PCD may be chamfered, double chamfered or multiple chamfered.

Each PCD may comprise a polished cutter surface, or be at leastpartially polished.

Alternatively, rather than being a traditional PCD, the cutting element22 may be a 3-D shaped cutter. A strike tip of the cutting element 22may be conical, pyramidal, ballistic, chisel-shaped or hemi-spherical.The strike tip may be truncated with a planar apex, or non-truncated.The strike tip may be axisymmetric or asymmetric. Any shape of cuttingelement 22 could be used, in combination with any aspect of thisinvention. Examples of such shaped cutters can be found in WO2014/049162and WO2013/092346.

In a first embodiment of a tool holder 24, in FIGS. 5, 6 and 7, eachtool holder 24 is generally frusto-conical when viewed axially (see FIG.6). Each tool holder 24 has a leading face 26 and a trailing face 28,each cutting element 22 being received into a seat 30 in the leadingface 26 of the tool holder 24. Each seat 30 is angled such that thecutting element 22 tangentially faces (or generally points towards) theintended direction of rotation. This is particularly useful for PCDswhich have a planar primary cutting surface 32. Thanks to the seat, acutting edge 33 of the cutting element 22 can be oriented in a range ofangles with respect to the cutter body 20, which contrasts with theconventional approach of having cutting elements 22 pointing exclusivelyradially or axially outwards in the direction of advance of the rockface. This allows great flexibility for obtaining a desired cuttingangle without having to modify the configuration of the strike tip ofthe cutting element.

Furthermore, having a seat for receiving a separate cutting element 22means that advantageously, any surplus PDC stock can be used up and findutility in a new application, thereby reducing the working capital of acompany.

Optionally, the rake angle of the cutting element is between 25 degreesand 30 degrees. optionally, the rake angle is around 25 degrees.Optionally, the rake angle may be positive or negative.

The leading face 26 of the tool holder 24 is generally shorter than thetrailing face 28, thereby providing significant structural back supportfor the cutting element 22 during use. The tool holder 24, particularlythe rear of the tool holder 24 in the direction of rotation, absorbs asignificant proportion of the impact forces during use, and reduces therisk of the cutting element 22 otherwise popping out of the cutter body20 and being lost.

Preferably, the seat fully supports the rear (i.e. the surface that isgenerally opposite the cutting surface 32) of the cutting element 22.

In side view (see FIG. 7), each tool holder 24 has a varying lateralcross-section, indicated by arrow B. Each tool holder 24 taperslaterally inwardly from the head 34 of the tool holder 24 near thecutting element 22 to a foot 36, near the circular body 20.

A lateral extent (best seen in FIG. 7) of each cutting element 22 isgreater than a lateral extent of the tool holder 24. This overhangprotects the tool holder 24 from significant wear during use.Preferably, a thickness (i.e. lateral extent) of the tool holder 24 isaround 14 mm.

In this embodiment, the cutting element 22 protrudes past the toolholder 24 by approximately 1 mm on either side. This ensures that it isthe cutting element 22, and not the tool holder 24 or the cutter body20, which is subject to the primary wear during use. The overhangprevents the tool holder 24 from rubbing against the rock formation 2.In the event of rubbing, a hard coating or multi-layered approach may beused.

In a second embodiment of a tool holder 24, as shown in FIGS. 8 and 9,successive tool holders 24 are laterally offset with respect to thecutter body 20. As indicated in FIGS. 10a and 10b , each tool holder 24includes a slight kink to one side. In other words, a distal portion 24a of the tool holder 24 is laterally offset with respect to the circularbody 20 and a proximal portion 24 b of the tool holder 24. Both thedistal and proximal portions 24 a, 24 b are laterally elongate. Thedistal and proximal portions 24 a, 24 b of the tool holder 24 meet at anintersection, indicated generally at 38. The direction of the lateraloffset is in either a first direction, axially away from one side of thecutter body 20, or in a second opposing direction, away from the otherside of the cutter body 20. In FIG. 10a , the tool holder 24 kinksrightwards and in FIG. 10b , the tool holder 24 kinks leftwards. Theintersection 38 may be a sharp change of direction, such as a dog leg,or a prolonged change of direction, such as a curve. The intersection 38may comprise a mid-portion joining the distal portion 24 a to theproximal portion 24 b.

As an alternative, it is envisaged that the proximal portion 24 b couldbe laterally offset with respect to the cutter body 20 whilst the distalportion 24 a is in alignment with the circular body 20. However, sincethe cutting element 22 is usually located on the distal portion 24 a ofthe tool holder 24, the first mentioned arrangement is preferable.

Along the circumferential surface 40 of the cutter body 20, thedirection of the lateral offset alternates for successive tool holders24. The benefit of this arrangement is that it increases the effectivecutting area offered by the cutting elements 22 during rotation of thecircular body 20, regardless of the size of the cutting element 22. Italso facilitates a quick and easy change of an individual tool holder 24during maintenance and repair, without having to remove the entirecutter body 20. Furthermore, the arrangement helps reduce erosion of thecutter body 20 (sometimes known as ‘body wash’) caused by the flow ofcut rock past the cutting assembly 10.

The cutting assembly 10 may additionally comprise a hard-facing material(not shown). The hard-facing material may comprise a low melting pointcarbide (LMC) material, characterised by its iron base. Exemplarymaterials are described in U.S. Pat. Nos. 8,968,834, 8,846,207 and8,753,755, although other wear resistant materials could be usedinstead. The purpose of the hard facing material is to limit body washof the circular body 20. The hard-facing material may be locatedrotationally behind the tool holder 24, proximate to the trailing face28. If the tool holders 24 are spaced apart, then the hard-facingmaterial may be provided in or on the cutter body 20, between successivetool holders 24. Additionally, or alternatively, the hard-facingmaterial may be provided on the trailing face 28. Additionally, oralternatively, the hard-facing material may be provided on the leadingface 26. The hard-facing material may be provided on the leading face26, the trailing face 28 and on the circumferential surface 40. Thelocation of the hard-facing material on the cutter body 20 and/or toolholder 24 is site specific, and is selected according to the nature ofthe rock formation being mined at that site.

In use, the disk cutter 18 is brought into contact with the rockformation 2 and rotation of the drive spindle 16, and therefore its diskcutter(s) 18, causes slicing of the rock formation 2. The cuttingassembly 10 slices into the rock formation 2, for example, to createclean orthogonal cuts of around 16 mm, depending on the size of thecutting elements 22 selected. The cut rock breakouts either under itsown weight or with secondary wedge force, e.g. using a wedge-shapedtool.

Although several applications of the cutting assembly have beenmentioned above, tunneling is a particularly attractive application.Conventionally, in order to create a new tunnel underground, a tunnelboring machine (TBM) is used. TBMs create a cylindrical shaped tunnel ina well-known manner. If the purpose of the tunnel is for vehicular orpedestrianised traffic, and only a circular lateral cross-section ispossible, a new horizontal floor must be included within the lowerportion of the tunnel. Effectively, the diameter of the tunnel isoversized. Excess rock material must be extracted in order to create theactual required useable space within the upper portion of the tunnel andthis increases tunneling costs, not only because a larger TBM demandsmore consumable cutting tips than s smaller TBM, but also that thetunneling operation takes significantly longer. Furthermore, additionalmaterial is required for construction of the new floor. Thanks to thecutting assembly described herein, a tunnel with a smaller lateralcross-section can be created, thereby producing the required shape ofthe upper tunnel. The cutting assembly then follows the smaller TBM toshape the lower half of the tunnel, creating a floor perpendicular tothe walls, and removing significantly less material than with a largerTBM.

While this invention has been particularly shown and described withreference to embodiments, it will be understood by those skilled in theart that various changes in form and detail may be made withoutdeparting from the scope of the invention as defined by the appendedclaims.

For example, in the second embodiment of the cutting assembly, thoughonly a single support arm 14 has been described, two or more spacedapart supports arms 14 may be provided instead.

For example, the two embodiments described herein both include aplurality of disk cutters 18 mounted on the drive spindle 16. This neednot be the case and a single disk cutter 18 could be used instead.

For example, instead of using a combination of paired cutting elements22 and tool holders 24, the cutting elements may be integrated directlyinto the body of the disk cutter 18 at a peripheral edge thereof,thereby obviating the need for an intermediate tool holder 24.

For example, the or each cutting element may comprise single crystaldiamond instead of polycrystalline diamond material.

For example, the cutting element 22 may comprise diamond or abrasivegrit impregnated metal or be ceramic based.

Although, the cutting assembly 10 has been described as been of beingutility underground, it may equally be used above ground, for example inan open quarry.

Furthermore, a smaller scale version could be used for digging microtrenches in roads and pavements, for example, for laying small diameterfibre optic cables. In this case, the cutting assembly 10 would becutting into asphalt and concrete, not rock. In such an embodiment, thediameter of the cutter body 20 would be in the order of 300 mm, thelateral thickness of the cutter body up to 20 mm, and the cuttingelements sized correspondingly. The intention is to achieve a depth ofcut of around 50 mm to 100 mm.

Certain standard terms and concepts as used herein are briefly explainedbelow.

As used herein, polycrystalline diamond (PCD) material comprises aplurality of diamond grains, a substantial number of which are directlyinter-bonded with each other and in which the content of the diamond isat least about 80 volume percent of the material. Interstices betweenthe diamond grains may be substantially empty or they may be at leastpartly filled with a bulk filler material or they may be substantiallyempty. The bulk filler material may comprise sinter promotion material.

PCBN material comprises grains of cubic boron nitride (cBN) dispersedwithin a matrix comprising metal, semi-metal and or ceramic material.For example, PCBN material may comprise at least about 30 volume percentcBN grains dispersed in a binder matrix material comprising aTi-containing compound, such as titanium carbonitride and or anAl-containing compound, such as aluminium nitride, and or compoundscontaining metal such as Co and or W. Some versions (or “grades”) ofPCBN material may comprise at least about 80 volume percent or even atleast about 85 volume percent cBN grains.

1. A cutting assembly for a rock excavation machine comprising: a baseunit, one or more moveable support arms extending from the base unit, adrive spindle rotatably mounted to the or each moveable support arm, adisk cutter fixed about the drive spindle such that rotation of thedrive spindle causes a corresponding rotation of the disk cutter, thedisk cutter comprising a cutter body, a plurality of cutting elementsand a corresponding quantity of tool holders, one for each cuttingelement, the cutting elements and tool holders being arranged around acircumferential surface of the cutter body, in which each tool holder isat least partially laterally offset with respect to the cutter body. 2.The cutting assembly as claimed in claim 1, in which successive toolholders around the circumferential surface are laterally offset inalternating first and second directions.
 3. The cutting assembly asclaimed in claim 1, each tool holder comprising a proximal portion and adistal portion meeting at an intersection.
 4. The cutting assembly asclaimed in claim 3, in which the distal portion is laterally offset withrespect to the proximal portion.
 5. The cutting assembly as claimed inclaim 3, in which each cutting element is mounted in the distal portionof the tool holder.
 6. The cutting assembly as claimed in claim 1,further comprising hard-facing material on or near each tool holder. 7.The cutting assembly as claimed in claim 6, in which the hard-facingmaterial is different to material of each cutting element.
 8. Thecutting assembly as claimed in claim 6, in which the hard-facingmaterial is located on a leading face of each tool holder.
 9. Thecutting assembly as claimed in claim 6, in which the hard-facingmaterial is located on a trailing face of each tool holder.
 10. Thecutting assembly as claimed in claim 6, in which the hard-facingmaterial is located on or in the circumferential surface of the circularbody.
 11. The cutting assembly as claimed in claim 1, in which eachcutting element has a strike tip having a conical or pyramidal profile.12. The cutting assembly as claimed in claim 1, in which each cuttingelement has a strike tip having a hemi-spherical profile.
 13. Thecutting assembly as claimed in claim 1, in which each cutting elementhas a strike tip having a ballistic profile.
 14. The cutting assembly asclaimed in claim 10, in which each cutting element has a truncatedstrike tip with a planar apex.
 15. The cutting assembly as claimed inclaim 1, in which each cutting element is a polycrystalline diamondcompact (PDC).